Communication is an integral part of modern society and provides the backbone of many services used on a day-to-day basis. An important component of any communication system is the transmission medium. Initially, such mediums of communication were accomplished using traditional metallic cables.
As the demands on the communication mediums have increased and with the advent of digital high bandwidth communications, it became desirable to make communication mediums that experienced lower loss, carried more data, and required less power to operate. One such approach to a low loss, high bandwidth communication medium is the optical fiber. The optical fiber provides an advantageous communication medium since it experiences less loss, can carry much more data per second than the typical metallic wire, and is immune to electromagnetic interference.
As fiber optic applications have become more prevalent, optical fibers are used in many complex devices and systems. In these applications, it is often desirable to couple optical fibers together, i.e. directing a portion of the light propagating in one optical fiber into another. This coupling may take the form of a simple broadband coupler of a fixed coupling ratio or, for more sophisticated wavelength division multiplexed fiber optic communication systems, a wavelength selective coupler that can be used to divert certain wavelength signals onto one fiber while leaving the remaining wavelength signals on the original fiber. A typical device used in these systems for coupling light between optical fibers is the fused fiber coupler. The fused fiber coupler is formed by placing two optical fibers in contact with one another and elongating the fibers while applying heat sufficient to soften the fibers. For example, U.S. patent application Ser. No. 11/473,689 to Harper et al., also assigned to the present application's assignee, discloses a method for controlling the shape of the fused fiber coupler through coordinated motion of a short heat source and an elongation apparatus.
An element of any optical fiber coupling/tapering system is the optical fiber heater. For example, the optical fiber heater may comprise a crucible including a heating element therein. Of course, the heating element must achieve a temperature within the crucible that exceeds the point at which silica (SiO2) is viscous, which is 1000° C. (1832° F.) (silica melting point 1650° C. (3002° F.)). The crucible includes an opening for receiving the optical fiber. The optical fiber is heated therein and drawn for tapering thereof. For coupling, two or more optical fibers are inserted through the opening and are held in contact with one another for fusion. Advantageously, optical fiber heaters that heat a short length (<3 mm) of optical fiber are desirable for fabricating high performance fiber optic devices.
An approach to optical fiber heaters is the flame based optical fiber heater, for example, as disclosed in U.S. Pat. No. 4,869,570 to Yokohama et al. The flame may be generated using Hydrogen or Deuterium, for example. Another approach to optical fiber heaters is the laser based optical fiber heater, for example, as disclosed in U.S. Pat. No. 7,266,259 to Sumetsky. In this approach, the optical fiber is heated indirectly using a carbon dioxide (CO2) laser to heat a sapphire tube through which the optical fiber is threaded.
An approach to optical fiber heaters is the filament based optical fiber heater, for example, as disclosed in U.S. Pat. No. 4,336,047 to Pavlopoulos et al. Using the same principle as filament based light bulbs, this heating device runs an electrical current through a tungsten filament in an argon atmosphere with the optical fiber directly exposed to the tungsten filament. Another approach to filament based optical fiber heaters is disclosed in U.S. Pat. No. 4,879,454 to Gerdt. This optical fiber heater uses several platinum filaments in an alumina support structure to radiatively heat the optical fiber. In this approach, the optical fiber is directly exposed to the platinum filament. Another approach to electric resistance based optical fiber heaters is disclosed in U.S. Pat. No. 6,701,046 to Pianciola et al. This optical fiber heater uses a cylindrical platinum crucible that is heated by radio frequency (RF) induction.
Another example of an electric resistance based optical fiber heater is available from the Micropyretics Heaters International Inc. of Cincinnati, Ohio and includes the typical crucible having an opening and a heating element therein. The heating element comprises an electric resistance heating element made from molybdenum disilicide. The crucible is made from a cast ceramic with the molybdenum disilicide heating element cast within the crucible body
Another approach to optical fiber heaters is the plasma based optical fiber heater, for example, as disclosed in U.S. Pat. No. 6,994,481 to Chi et al. Using similar operating principles to fusion splicers, these heaters create plasma from an electric discharge in air to heat the optical fibers directly.